1. Field of the Invention
The present invention generally relates to a method for improving the resolution of optic lithography, and more particularly to an ultraviolet light illumination method for treating the photoresist layer.
2. Description of the Prior Art
Lithographic processes are used in manufacture of semiconductor devices, such as integrated circuit chips and read/write heads for magnetic media drivers, e.g. disc drives and tape drives. Lithographic processes typically involve a step of depositing a layer of a photo resist material onto a device such as a silicon wafer by e.g. spin-coating. Next comes a selectively exposing portion of the photo resist layer to radiation, e.g. ultraviolet, X-ray or ion or electron beam. The last step includes developer solution, e.g. tetramethylammonium hydroxide (TMAH), thereby removing the non-irradiated portions of a negative photo resist or irradiated portions positive photo resist.
The modern semiconductor industry""s continuing drive toward integrated circuits with ever decreasing geometries, coupled with its pervasive use of highly reflective materials, such as polysilicon, aluminum, and metal suicides, has led to increase the photolithographic patterning problems. Unwanted reflections from these underlying materials, during the photoresist patterning process, cause the resulting photoresist patterns to be distorted.
This problem is further compounded when photolithographic imaging tools having ultraviolet (UV) and deep ultraviolet (DUV) exposure wavelengths are used to generate the photoresist patterns. Although shorter wavelengths bring improved resolution by minimizing diffraction limitations, and resulting patterns generated in the photoresist are easily compromised by the effects of uncontrolled reflections from underlying materials due to the increased optical metallic nature of underlying reflective materials at these wavelengths. Moreover, photoresist patterns are particularly degraded in areas where the topology of the underlying reflective material changes. In these stepped areas, the reflection intensity from underlying materials is often enhanced and results in a locally distorted photoresist pattern near the stepped areas. Therefore, the formation of sub-micron photoresist patterns over semiconductor substrates is difficult to achieve, and as a result, fabrication of advanced integrated circuits with sub-micron geometries is limited.
In conventional wafer patterning process, the organic polymer type photosensitivity material is used as a media for mask pattern transferred through etching process to wafer. But the integrity of organic polymer type photosensitivity material will nit be maintained, due to the short wavelength radiation such as deep UV is illuminated to organic photo resist layer, the chemical bond of organic photo resist layer is broken by photochemical reaction. Such that the cost of photo resist layer is increased. The other disadvantages are that the optic lithography is in order to improve the resolution of optic lithography by reducing wavelength of illumination. When the radiation wavelength is lower, the organic polymer photoresist will be degraded, the out-gassing is generated, and the lens of exposure tools is contaminated and the resolution of optic lithographic is degraded.
It is an object of this invention to use an inorganic photoresist layer formed on the wafer to avoid the chemical bond is broken by illumination.
It is another object of this invention to improve the out-gassing during the fabrication for optical lithography process.
It is still another object of this invention to improve the resolution of optical lithography process.
It is still another object of this invention to reduce the cost of photoresist layer in the integrated circuit fabrication.
In accordance to above-mentioned objects, in one preferable embodiment, an etched layer, an inorganic photoresist layer, and an atomic layer are sequentially formed on a substrate. Then, an ultraviolet light is illuminated through the reticle to the inorganic photoresist layer. The chemical bond of inorganic photoresist layer cannot be broken, and the out-gassing will not be occurred. The inorganic photoresist layer is produced acid molecular after illumination and the acid molecular is used to catalyze the atomic layer. Then, the atomic layer under exposure area has oxidation with active oxygen atom after catalyze. After oxidation, the oxide pattern can be obtained and the etching process is easy to etch and no out-gassing is generated.